This invention relates to a plasma processing apparatus such as a plasma etching apparatus used for dry etching semiconductor integrated circuits, and a plasma processing method.
Semiconductor integrated circuits have become more and more miniaturized and complicated to satisfy requirements for higher functions and higher operation speeds. In plasma processing apparatuses for processing such semiconductor integrated circuits, as disclosed in JP-A-2-65131, it has conventionally been known to prevent electrostatic damage of a wafer by disposing a ring having electric conduction around an outer periphery of the wafer.
However, the conventional technology described above is not yet entirely satisfactory for preventing electrostatic damage in gate oxide films the thickness of which has become smaller and in those wafers the diameter of which has become greater such as 12 inches or more. This technology cannot either reduce entirely sufficiently electrostatic damage that changes depending on process conditions varying to large extents.
The plasma etching technologies for processing semiconductor circuits according to the prior art attempt to find out a compatible condition that does not invite damage depending on process parameters but provides good shape processability, and conduct the dry etching process.
However, a process window having high shape processability has become small as the semiconductor devices have become miniaturized and have come to possess a higher aspect ratio while the diameter of the wafers to be processed has become greater. Therefore, it is difficult according to the prior art technologies described above to simultaneously satisfy a process window free from damage and a high processing factor such as a processing rate without their trade-off.
Barns et al U.S. Pat. No. 5,535,507 discloses an electrostatic chuck for supporting a workpiece by electrostatic attraction between the workpiece and an electrode for installing the workpiece, and offsetting etching non-uniformity of the workpiece. However, this reference does not teach or suggest means for preventing a defect due to xe2x80x9ccharging damagexe2x80x9d of the workpiece.
JP-A-8-316212 discloses another technique in which an electrode portion of a wafer mount is divided into a plurality of electrically isolated areas, impedance matching elements are connected to respective areas so as to control the impedances thereof, and alternatively, a recessed portion is provided on the electrode surface of the wafer mount such that the impedances between the wafer and the electrode differ between the center portion and the outer portion of the electrode to make ion energy emitted to the wafer uniform over the entire surface, thereby achieving a uniform plasma process.
As disclosed in JP-A-8-181107, there is known a technique that a surrounding ring formed of ceramic is provided around a lower electrode, a wafer is mounted on the surrounding ring so as to have a space between the wafer and the lower electrode and thereby have an electrostatic capacitance, so that a DC voltage generated in a plasma is distributed into the space, a blocking capacitor and the wafer to prevent occurrence of charging damage to the wafer.
However, both of the techniques do not make reference to the compensation for the charging damage of the workpiece which the present invention intends to solve.
It is therefore an object of the present invention to provide an apparatus and a method capable of plasma-processing high-speed semiconductor devices, that are susceptible to damage due to charge-up, on a wafer having a large diameter with an increased yield.
It is another object of the present invention to provide a combination of an electrode structure for installing a workpiece, such as a wafer, with a circuit, the combination being for use in an apparatus and a method capable of plasma-processing high-speed semiconductor circuits with an increased yield.
According to one aspect of the present invention for accomplishing the objects described above, an insulating material covering an entire surface of an electrode opposing the back of a workpiece (wafer) is thicker at a part thereof than at other portions, and an electrode is separately disposed inside the insulating material. A bias current is supplied to the electrode, and the amount of the bias current is regulated.
In other words, according to one aspect of the present invention, there is provided a plasma processing apparatus so constituted as to be able to apply bias power to a workpiece, wherein a feed impedance difference of bias power to a plurality of positions inside the workpiece is variable.
According to another aspect of the present invention, there is provided a plasma processing apparatus, wherein an insulating film is interposed between a workpiece installing electrode and a workpiece, the insulating film has at least two kinds of thickness, at least one kind of the insulating film contains an electrically conductive material, and the conductive material is connected to a bias power feed line insulated from the electrode.
According to still another aspect of the present invention, there is provided a plasma processing apparatus including a workpiece installing electrode and an insulating film interposed between the electrode and a workpiece, wherein the insulating film is made of at least two kinds of materials, at least one kind of the insulating film contains an electrically conductive material, and the conductive material is connected to a bias power feed line insulated from the electrode.
According to still another aspect of the present invention, the impedance of the bias power feed line of the plasma processing apparatus described above is variable or a power supply circuit for electrostatic attraction is connected to the bias power feed line.
In a plasma processing apparatus for converting a raw material gas to plasma and plasma-processing a surface of a workpiece, including a vacuum vessel having exhaust means, raw material gas supplying means, installing means for installing a workpiece such as a wafer, and means for applying radio frequency power to the workpiece, still another aspect of the present invention provides an electrode structure including a bias circuit for use in the plasma processing apparatus, wherein an insulating film is interposed between an electrode for installing the workpiece and the workpiece, the insulating film has an electrically conductive material disposed at a part thereof; and the conductive material is electrically grounded.
According to still another aspect of the present invention, the conductive material in the insulating film interposed between the workpiece and the electrode described above is electrically grounded through an impedance variable device.
According to still another aspect of the present invention, the conductive material in the insulating film described above is electrically connected to the electrode for installing the workpiece through the impedance variable device.
According to still another aspect of the present invention, there is provided a method for plasma-processing a workpiece wherein a set value of the impedance variable device described above is adjusted in accordance with a dielectric breakdown pattern that occurs in the workpiece.
In another aspect of the present invention, a plasma processing apparatus for processing a wafer as ions in a plasma are induced, comprises a wafer-installing stage on which the wafer is installed; an wafer-installing surface of said stage electrically isolated; a circuit connected with the electrically isolated wafer-installing surface supplied with a bias power; and adjusting means for making equally adjustable an impedance of the circuit through which a current flows from each position on said wafer to the ground through said wafer and said plasma.
In a further aspect of the invention, a plasma processing apparatus comprises: a workpiece-installing stage electrically insulated from a grounded vacuum vessel; said stage including a first electrode forming a base, an insulating film provided on said first electrode and having its outer peripheral portion thicker than the thickness of its center portion and a second electrode provided within the outer peripheral portion of said insulating film and at a position having the same thickness as the center portion of said insulating film, said first electrode being connected to a radio frequency power supply; and an impedance adjuster electrically connecting said first electrode and said second electrode.
In the above-plasma processing apparatus, said insulating film includes a first insulating film provided between said first electrode and said second electrode and a second insulating film provided on a side of workpiece-installing surface.
In still another aspect of the invention, a plasma processing method of processing a wafer while inducing ions in a plasma thereto, comprises the steps of: changing an impedance of each position on a wafer installing surface of a workpiece-installing stage on which the wafer is installed during a plasma process such that the bias potential difference within the wafer surface through the plasma at a plurality of said positions due to bias voltages applied to the wafer is reduced to a breakdown voltage of transistors formed on said wafer or less; and subjecting said wafer to a plasma process.
In a further aspect of the invention, a plasma processing method for a substrate of a wafer, comprises the steps of: causing a value of an applied self bias voltage (Vdc) at each position within the surface of a wafer minus an average of the applied self bias voltage (Vdc) within the surface of the wafer to indicate a minus value, and adjusting an impedance of a position on the wafer in which an absolute value of said minus value is larger, so as to increase.
Other objects, features and advantages of the present invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.